This invention relates to a method and apparatus for inserting a weft into the warp shed of an air jet loom by ejecting compressed air with the weft.
In the air jet loom of the prior art, as shown in FIG. 1, a weft W supplied from a source of weft (not shown) is first stored in a weft storing device 1 and then passed through a gripper 2, comprising gripping members having one member mounted for movement toward and away from the other to grip and release the weft W, and an ejection nozzle 3. The compressed air is ejected from the ejection nozzle 3 toward a weft guide passage formed by a number of guide members 6 arranged in an array at a predetermined interval(s) on the cloth fell side of a slay 4 with respect to a reed 5. The weft W is also ejected from the ejection nozzle 3 together with the compressed air and inserted through the guide passage. Thus, the weft insertion can be accomplished. The inserted weft is cut away from the weft source by a cutter (not shown) generally disposed between the ejection nozzle 3 and the edge of the cloth, after the beating by the reed 5 has been carried out.
As shown in FIG. 2, the ejection nozzle 3 comprises a substantially cylindrical nozzle body 9 fitted into a through hole 8 provided in a bracket 7, which may be fixedly mounted on a machine frame (not shown). To the forward end portion of the nozzle body 9, an accelerating tube 10 is connected by a nut 29, and in the other end of the nozzle body 9 a substantially cylindrical cavity 11 is provided to receive therein a needle 14 having a central weft guide passage 13 extending longitudinally within the needle 14. The needle 14 is connected with screw thereads to the wall of the cavity 11 as shown, and the cavity 11 is in fluid communication with the accelerating tube 10 through a passage 12 centrally provided in the nozzle body 9. An annular groove 15 is formed in the outer cylindrical surface of the rear end portion of the nozzle body 9. Radially extending air supply holes 16 are provided in the rear end portion of the nozzle body 9 so as to open at the radially outer ends thereof into the bottom of the annular groove 15 and at the radially inner ends into the cavity 11. As shown in FIG. 3, all the radial holes 16 extend perpendicular to the axis of the nozzle body 9. Around the annular groove 15, a sleeve 17 is provided and firmly supported on the nozzle body 9 by nuts 30 and 31 with the assistance of the bracket 7. The sleeve 17 is provided with a hole 18, which is in fluid communication with the annular groove and into which a pipe 19 is fixedly engaged to supply the cavity 11 with the compressed air. As diagrammatically shown in FIG. 4, the pipe 19 is connected through an electromagnetically or mechanically operated valve 21 to a compressed air tank 20. A by-pass pipe 22 by-passes the valve 21 and also connects the pipe 19 to the tank 20. In the by-pass pipe 22, a throttle valve 23 is provided.
The valve 21 opens in timed relation with the time period of the weft insertion to allow the compressed air in the tank 20 to be supplied through the pipe 19 into the ejection nozzle 3 thereby to cause the weft entrained in the flow of the compressed air to be inserted through the weft guide passage defined by the guide members 6. The valve 23 is always maintained in an opened condition except during the time period of the weft insertion so that the compressed air, reduced in pressure by the throttle valve 23, is supplied through the pipe 22 into the ejection nozzle 3 and therefore a gentle flow of air flows in the accelerating tube 10. By this gentle flow, the end of the weft W projecting out of the accelerating tube 10 even after the cutting of the inserted weft is slightly tensioned. Therefore, not only is the failure of cutting prevented, but also the weft insertion performance can be improved.
However, analysis of all the factors affecting the failure of the weft insertion showed that the breakage of the weft occurring in the ejection nozzle during the weft insertion constituted the decisive factor causing weft insertion failure. Also, it was an important factor that the end of the weft exposed to the afore-mentioned gentle air flow within the ejection nozzle was broken due to the gentle air flow. Because this breakage caused a shortage of weft length for the next weft insertion, the leading end of the weft could not reach the predetermined position.
The above-discussed two factors of weft insertion failure were created by the breakage of the weft in the ejection nozzle. In view of these facts, the inventors of the present invention attempted analysis of a weft's behavior in the ejection nozzle. As a result, it was found that, although the cylindrical weft passage in the ejection nozzle was fully confined circumferentially by the inner wall surface of the ejection nozzle, the weft portion present in the weft passage violently vibrated while rotating in an untwisting direction. This phenomenon caused the breakage of the weft in the ejection nozzle. Specifically, the rotation of the weft in the untwisting direction was caused by the fact that the flow of air in the ejection nozzle passed around the weft in frictional relation therewith at a speed higher than that of the weft (the weft is stationary except during the time period of weft insertion), thus squeezing the weft through the air flow, and subjecting the weft to a force rotating the weft in the untwisting direction, in addition to the propulsive force of the air flow, resulting in weft breakage.
Furthermore, where the weft is a filament yarn, the filaments are apt to be cracked by the violent vibrations and the rotation in the untwisting direction of the weft in the ejection nozzle. Even if the breakage of the filament yarn does not occur, the cloth woven by the yarn including the cracked filaments becomes lower in quality.
It is therefore understood that a weft inserting method and apparatus for a jet loom are required, which are free of the above-disadvantages of the prior art.